Method of and means for starting synchronous motors



March 29, 1932. D7 w, MCLENEGAN 7 1,851,716

METHOD OF AND MEANS FOR STARTING SYNGHRONOUS MOTORS Filed Feb. 12, 1930Inventor-z David W Mc Lenegan,

His Attorney Patented Mar. 2%, 1932 UNETED STATES reruns civics;

HAVE W. HCLENEGAH, F SC'EENEETADY, NEW YQEK, ASBIGNOR TO G'fihm ELECTRICcomm, A COEPQBATIQE @F NEW YQEK MEEEQD OF onetime FQE, 'EABTIBZGSYE'CEEAJEEQUS Applieetlon filed Elelsrnury 12, 936}. 15o. sense-v,

My invention relates to the starting of e ilchronous motors, and hes forits object the provision of a simple end reliable method or and meansfor starting synchronous motors wherein a voltage higher then the normalrunning voltage is used.

' it is well known in the art to provide it synchronous motor with enauxiliary squirrel cuge winding on its rotor whereby the mo- 1o tor maybe started as an induction motor but without field excitation, and whenit has been brought up to synchronous speed, locked V in step byenergizing the field winding. This method of storting, however, has thedisadvantage that it rovides an inherently low starting torque or motorsof relatively low speeds, and consequently, when normal voltage only isused s low speed motor cannot be started under full load, orsubstantially full load, conditions. It has also been proposed toapply-en excess or higher then normal voltage to the motor on startingto im. rove its starting torque, but with this metho difficulty has beenencountered in reventing 2 the motor from slowing up and oiling out ofstep in the short interval while the corn nections are being changedfrom the excess voltage to the normal voltage. More pen,

ticulsrly, it is on ob ect of my invention to to provide an improvedmethod of and means for starting synchronous motors wherein theswitching operations from excess to normal voltage muy he curried outwithout (longer of the motor felling out of step.

in carrying out my invention in one form ll provide it stertincompensator croutotrensformer for opp ying an excess starting volts e,together with switching moons where y a winding of the compensetor mayhe connected us a reactor in the motor circuit while the motorisswitched from the excess starting voltsgeto the normal voltage.

For n more complete understanding of my invention, reference should behad to the eecompanying drawing, the single figure of which is ediagrammatic illustration of u stsrting system for synchronous motorsemhodying my invention.

Referring to the drawing, in one form of it my invention the synchronousmotor 10, provided with the ususl distributed armature winding on itsstator member and further provided with a direct current field windingor winding on its rotor member together a squirrel cage winding, orother suitable starting winding, on its rotor member, is sup plied withan excess voltage during the stert= ing period from the stsrtmgcompensator or autotransformer ll. lhe motor is shown us a. three-phasemotor since this is a, typical example, although it will he understoodthat, my invention is applicable to motors having different numbers ofphases. As shown, in termediete tops on the uutotrensi'ormer windings12, 13, and it may be connected through a switch 15 to e suitablethree-phase source of supply 16 having a voltage equal to t normalrunnin voltage of the motor. @ne terminal of one of the windings l2, 13,end it is connected directly to the motor. do ye shown the lowerterminals of these windings are connected respectively through theconductors i7, 18 end 19 to the three ermoture terminals of the motor,while the remuining terminals of the eutotrensrormer windings may beconnected together by moons oi a switch 20 whereby the windings areconnected in the well known Y connection. A switch 21 is providedwhereby the motor armature may be connected through the conductors 22,23, and 24 directly to the supply source it tor normal runningconditions.

A suitable interlock, shown as s Inechenicol interlock, is providedbetween switches 2d and 21 whereby neither switch can he close T whenthe other switch is closed or, in other words, only one switch can beclosed st any one time. As shown this interlock comprises a bar 25 whichis pivotebly connected to the switch 20 so as to be moved longitudinallytoward the right, as seen in the drawing, when the switch 20 is movedfrom the open position, as shown, to the left to the closed position.With the switch 21 open, the end of this bar moves into s notch orrecess 26 rovided for it in a, com 27 carried by switch 21 whereby theswitch 20 can be closed, but when the switch 21 is closed, this barengsges the protruding or higher ed e of the cum to prevent the closingof the switch 20. It will 5% be understood that when the switch 21 ismoved to the left to the closed position, the cam 27 is rotated througha small an le with the switch so that its hi her position is in the pathof the bar 25. onversely, when the switch is closed, the switch 21 islocked against closure by the engagement of the bar 25 in the recess 26.The field circuit of the motor may be 'connectedto a suitable directcurrent source of supply 28 by means of a switch 29. As shown,capacitors 30 are provided to improve the power factor of the supplysource.

In the starting of the motor the switch 20 vis closed, the switch 21being open, to establish the Y connection for the autotransformer andthen the switch 15 is closed to apply an excess voltage from theautotransformer to the motor. At this time the switch 29 will be open sothat the field of the motor will be deenergized. When the motor hasaccelerated to substantially synchronous speed on the excess voltageconnections, theswitch 29 will be closedto energize the field of themotor, whereupon the motor will be pulled into step. Assuming that themotor has accelerated to the synchronous speed and has been locked instep, by the ener ization of its field winding, the next step in t estarting operation is the opening of the switch 20 whereby the'motorarmature is connected to the supply source 16 through portions of thewindings 12, 13, and 14, the lower portions as indicated'on the drawing,which ortions act as reactors and'while reducing t e volt-' age appliedto the motor somewhat, at the same time provide for suflicient voltageto hold themotor in step while the switch 21 is being closed which isdone as soon as possible after the switch 20 has been opened. Theclosing of the switch 21 connects the motor directly to the suppl sourcefor normal runchan 'ng from one voltage to the other. Am-

ple time is thus given for the change and there is little danger of themotor falling out of synchronism. It will be understood that it isassumed that the motor is started under load and consequently if it weredeenergized entirely during the switching operation, its speed woulddecrease very quickly to such an extent that the motor might fall out ofstep.

What I claim as new and desire to secure Lemme by Letters Patent of theUnited Statesis: 1. In a starting system for synchronous motors, a supplcircuit, a compensator, switching means Ior connecting said compensatorto supply avoltag'e in excess of the supply circuit voltage to the motorto accelerate the'motor to its synchronous speed and for connecting themotor to the supply circuit through a portion of said compensator actingas a reactor, and switching means for connecting the motor directly tothe supply circuit.

2. In a starting system for synchronous motors a supply. circuit, acompensator, switching means arranged in one position to connect saidcompensator to supply a voltage in excess of the supply circuit'voltageto the motor and in-another'position to connect the motor to the supplycircuit through a portion of said compensator acting as a reactor, andswitching means for connecting the motor'directly to the supply circuit3. In a. starting system for synchronous motors, a polyphase supplycircuit, a polyphase compensator connected to supply a voltage in excessof the supply circuit voltage to the motor, a switch arranged whenclosed to connect the windings ofsaid compensator together to supplysaid excess voltage to the motor and when open to connect the motor tothe supply circuit through portions of the compensator windings, and aswitch for connecting the motor directly to the supply cir cuit.

4. In a starting system for synchronous motors, a polyphase supplycircuit, a polyphase compensator connected to supply a voltage in excessof the supply circuit voltage to the motor, a switch arranged whenclosed to connect the windings of said compensator together to supplysaid excess voltage to the motor and when open to connect the motorto'the supply circuit through portions of the compensator windings, aswitch for connecting the motor directlyto the supply circuit, andinterlocking means between said switches.

5. In combination with a three phase synchronous motor provided with athree phase armature winding, of a three-phase supply circuit, a threephase compensator connected to said armature winding, a switch forconnecting intermediate points of said windings to said supply circuit,a switch for connecting the windings of said compensator in .Y, wherebya voltage in excess of the supply circuit voltage is applied to saidarmature winding, a switch for connecting said armature winding directlyto the supply circuit, and interlocking means between the latter twoswitches whereby one can be closed only when the other is open.

6. The method of starting a synchronous motor from a supply circuitwherein a starting compensator is used which consists in hand this 11thda

